Recently, with the development of the solid state imaging device, there has been developed an electronic endoscope whereby a body cavity interior is imaged with a solid state imaging device such as a charge coupled device (CCD) contained in the tip part of the endoscope. The picture image from the solid state imaging device is displayed by an external displaying device.
Usually, the light source of an endoscope is provided as a light source device separate from the body. The endoscope is connected to the light source device through a light source connector branched from the body. The illuminating light from the light source device is radiated onto an object to be imaged through a light guide fiber bundle.
In an electronic endoscope such as described above, a driving pulse generating circuit for generating driving pulses for driving the solid state imaging cevice and a video image processing circuit for videoprocessing the picture image signals from the solid state imaging device are required. Usually, these circuit units are provided within a video processor separate from the endoscope body the same as in the light source device. The driving pulses to the solid state imaging device are fed to the solid state imaging device through signal lines within the endoscope body.
Generally, endoscopes of various lengths and diameters are prepared depending on the position in which the endoscope is to be inserted. The same solid state imaging device is used for any kind of electronic endoscope so that such a circuit unit may be used in common for any kind of electronic endoscope. However, if the length of the endoscope is different, the distance of the signal line from the circuit unit within the light source device to the solid state imaging device at the tip of the endoscope will also be different in response to it and have a disadvantage such in the following. Generally, when the length of the signal transmitting line becomes longer, the waveform of the clock pulse fed to the solid state imaging device from the driving circuit will distorted and will be no longer be an accurate rectangular waveform and the solid state imaging device will not be accurately driven. The influence of the distortion of the waveform while transmitting this signal is different with the length of each endoscope. Therefore it has been impossible to connect a plurality of electronic endoscopes of different lengths to the driving circuit of one unit.
Therefore, with a formation such as shown in FIG. 1, the waveform distortion of clock pulses by the difference of the length of the endoscope, that is, the distance of the signal line from the video processor to the solid state imaging device in the tip part of the endoscope has been compensated.
In FIG. 1, in the tip part of the endoscope 10, a charge coupled device (CCD) 12 as a solid state imaging device is contained to image a body cavity interior. The illuminating light from a light source device 14, separate from the endoscope 10, is to illuminate the body cavity interior through a light guide fiber bundle 16. The light source 14 has a light source lamp 18 and a lens 20 condensing the light from the light source lamp 18 to the end of the light guide fiber bundle 16.
On the other hand, the signal obtained from the CCD 12 in the tip part of the endoscope 10 is fed to a video signal processing circuit 28 through a differential amplifier 26 within a video processor 24. The output of the video signal processing circuit 28 is displayed by a displaying device (for example, a CRT display) 30.
The video processor 24 is further provided with a driving pulse generating circuit 32 and a constant voltage source circuit 34. The output signal of the constant voltage source circuiut 34 is fed as a substrate bias voltage V.sub.sub to the CCD 12. The driving pulse generatign circuit 32 generates horizontal driving pulse .phi.H.sub.1 and .phi.H.sub.2, a resetting pulse .phi.R and vertical driving pulses .phi.V.sub.1 and .phi.V.sub.2. The horizontal driving pulses .phi.H.sub.1 land .phi.H.sub.2, resetting pulse .phi.R and vertical driving pulses .phi.V.sub.1 and .phi.V.sub.2 are fed to the CCD 12 respectively through horizontal driving circuits 40 and 42, a resetting pulse driving circuit 44 and vertical driving circuits 46 and 48. The respective driving circuits 40, 42, 44, 46 and 48 are circuits amplifying the voltages of the respective pulses to predetermined voltages.
As the waveforms are distorted during the transmission through signal lines, the horizontal driving pulses .phi.H.sub.1 and .phi.H.sub.2 and resetting pulse .phi.R are fed respectively to waveform compensatign circuits 50, 52 and 54 for compensating the waveform distortions in advance. The waveform compensating circuits 50, 52 and 54 are to differentiate the input pulses and to superpose them on the driving pulses so that, when reaching the CCD 12, the driving pulses will be accurate rectangular waves. Here, in order that the video processor 24 may be connected to a plurality of endoscopes of different kinds (lengths), the respective waveform compensating circuits are provided with a plurality of differentiating circuits of different time constants. Input pulses are input into respective differentiating circuits, the outputs of all the differentiating circuits are fed to switching circuits 56, 58 and 60 and any one signal is selected by the kind (length) discriminating signal of an endoscope not illustrated. The switching circuits 56, 58 and 60 are provided with relay switches or the like connected to the outputs of the respective differentiating circuits.
As the vertical driving pulses .phi.V.sub.1 and .phi.V.sub.2 are signals of frequencies lower than of the horizontal driving pulses .phi.H.sub.1 and .phi.H.sub.2 and resetting pulse .phi.R, the influence of the waveform distortion during the transmission through signal lines will be low. Therefore, no waveform compensating circuit is provided here.
Now, according to the above mentioned formation, if the kinds of the endoscope are n kinds, 3n differentiating circuits and 3n relay switches will be required. Thus, the video processor 24 has come to be large and the cost has been high.
Further, due to the fluctuation in the production of the CCD, the optimum voltage value of the direct current voltage (V.sub.sub) fed to the CCD 12 is different with the devices. However, heretofore, it has been set at a representative voltage by neglecting this difference. Therefore, the performance of the CCD 12 has not been able to be well developed.
In U.S. Pat. No. 4,667,229, it is shown that an endoscope includes a means of generating a signal discriminating the parameter value, a controlling device connecting the endoscope includes a means of responding to the above mentioned parameter discriminating signal and various endoscopes can be used. However, in this prior art, no driving pulse waveform compensating means is provided.